Hydrocarbons, such as oil and gas, may be recovered from various types of subsurface geological formations. Such formations typically consist of a porous layer, such as limestone and sands, overlaid by a nonporous layer. Hydrocarbons cannot rise through the nonporous layer, and thus, the porous layer forms a reservoir in which hydrocarbons are able to collect. A well is drilled through the earth until the hydrocarbon bearing formation is reached. Hydrocarbons then are able to flow from the porous formation into the well.
In practice, however, production from a natural gas well is rarely that simple. Many formations are minimally porous and do not readily allow gas to flow from the formation to a well bore. Thus, various strategies have been devised for enhancing the flow from such formations, including “horizontal” drilling and “fracking” the formation. That is, instead of drilling more or less vertically through a more or less horizontally oriented formation, techniques have been developed which allow a well bore to be drilled horizontally along a formation. This greatly increases the exposure of the well bore to a formation and, therefore, reduces the distance gas must travel through the formation in order to reach the well bore.
“Fracking” is another technique designed to increase the flow of gas from a formation. It involves drilling one or more “injection” wells in the vicinity of the “production” well through which natural gas eventually will be produced. Water and sand then are pumped through the injection wells into the minimally porous formation at very high pressures such that the injected fluid is encouraged to flow toward the “production” well. This process tends to “fracture” the formation, i.e., to open up pores and create flow paths from the formation to the production well.
While such techniques are very effective at ultimately increasing the flow of natural gas from a minimally porous formation, they create immediate challenges that must be met. In particular, the large quantities of water, sand, and other liquid and particulate additives that are injected into the formation during fracking eventually must be allowed to flow out of the formation. Also, since the well bore is passing horizontally through a fractured formation, the amount of particulate matter falling out from the formation itself is much greater than would be encountered with a vertical well or from an unfractured formation. The vast majority of the water and sand eventually will pass out of the well and the stream flowing from the production well will be relatively clean to natural gas. During the initial phase of production from such wells, however, the stream is typically a liquid dispersion containing not only natural gas, but also large quantities of water, sand, and any other additives that were injected into the well during fracking. That water and sand must be removed in order to process the natural gas and render it suitable for distribution and use.
It also will be appreciated that it is important to achieve effective removal of both water and sand from a production stream. Natural gas must pass through a variety of processing equipment and transmission pipelines before it is actually used. Entrained sand can be very corrosive to such systems, especially the various valves, chokes, and dryers typically incorporated into such systems. Liquid water also is corrosive, particularly as it may absorb various chemicals originating in the well that can render it acidic. Since the gas typically will experience pressure drops as it is processed and transported, water vapor will condense in the system unless it has been reduced.
Conventional apparatus, commonly referred to as sand separators, typically are cylindrically shaped, vertically oriented vessels. A production stream is introduced at the upper end of the vessel through an inlet port. The interior of the vessel is sized to allow the production stream to experience a sufficiently large velocity drop such that natural gas will separate. A vertical divider plate, which typically extends down the middle of the cylinder between the inlet port and the gas port for approximately ¾ of the length of the cylinder, forces fluid flow past a drain located at the bottom of the cylinder. The water and sand components of the stream are allowed to exit the bottom of the vessel through the drain while the gas rises back to the top of the vessel and eventually out of the vessel via a gas port.
While such conventional sand separators have been generally effective where the production stream has relatively lower pressures and flow rates and has relatively little sand and water, they are not well suited to high pressure, high velocity streams containing relatively large quantities of sand and water as are more and more commonly encountered. Such separators allow high pressure streams tend to blow out too much sand and water.
It also will be appreciated that sand separators typically are fabricated from cast steel and are on the order of 16 to 24 inches (O.D.) in diameter, 5 to 8 feet in length, and have wall thicknesses of from about 2 to 3 inches or more. Thus, the amount of material required for fabrication is substantial, as is the weight of such apparatus.